Process for reducing salt content of salt containing water



L. LAzARE 3,386,913

PROCESS FOR REDUCING SALT CONTENT OF SALT CONTAINNG WTER June 4, 1968 4Sheets-Sheet l Filed Dec. 50, 1965 o o o O lf) Do 3H nl VHd W31.

INVENTOR.

Leon Lazare ma, ATTORNEY scnss FOR REDUCING SAL? CONTENT oF SALTcoNTAINING WATER L. LAZARE June 4, 1968 4 Sheets-Sheet :3

Filed Dec. 50, 1965 NGI o. a mtssm PB A A June 4, 1968 L.. LAzAREPROCESS FOR REDUCING SALT CONTENT OF SALT CONTAINING WATER 4Sheets-Sheet (S CENTRIFUGAL EXTRACTOR PRODUCT f wAsH wATER/ wAsTEcoNceNTRATe 7o 7% SALT l June 4, 1968 L. LAZARE Filed Deo. 30, 1965FIG.6

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p LEAN SoLvENT 40% PoLYMER m A TL W \PR0DUCT IOO PPM SALT United StatesPatent 3,336,9i3 PROCESS EUR REDUQHNG SALT CONTENT @it SALT CNTAHNENGWA'lllilR Leon Lazare, Stamford, Conn., assigner to The Puraq Company,New York, NSY., a partnership Continuation-impart of application Ser.,No. 423,975, dan. 7, 1965., This application Ecc. 3G, 1965, Ser. No.5l7,625

17 Ciainisa for power, heat and chemicals, whereby to achievesubstantial reductions in processing costs, as well as simpiityingequipment requirements so as to also reduce capital investment per unitof treated water end product.

In known desalinating procedures of the multiple tiash evaporator orstill type; electrodialysis and freezing procedures, rand modificationsthereof, the required apparatus for handling large quantities of waterto 'be treated, involves substantial lcapital investment, as well ashigh operating costs for power, heat and refrigeration; all of which isreflected in relatively high overall costs per unit of water trelated.

Accordingly, a `further object of this invention is to provide animproved process of the character described wherein the system is ofsimple, economical construction; and the necessary lpower, heat andrefrigenation, and chemicals are minimal so as to leave the overall costper unit of water recovered, at -a val-ue materially less than thataccruing from the most efficient, known procedures.

A further object of this invention is to provide an improved process fortreating salt containing water wherein saline free water is continuouslyextracted from a continuous stream of salt containing water bycontacting the same with a lselected solvent having a large capacity forwater enrichment at a critical temperature related to the solvent; thewater enriched solvent being separable rat another temperature intosubstantially solvent free water and solvent phases, thereby providing apotable water product; while permitting the solvent phase to becontinuously recycled to continuously extract further amounts of waterof reduced saline content from the salt containing water.

Still another object of this invention is to provide in a process of thecharacter described, procedure for `effecting maximum recovery ofsolvent during the extractive operations so as to leave minimal amountsof solvent in the recovered water product and to minimize solvent lossesduring the extractive operations.

`Other objects of this invention will in part be obvious and in parthereinafter pointed out.

In the drawings, FIG. l is a diagrammatic showing of a process fortreating salt containing water, in accordance with the invention;

FIG. 2 is a showing similar to that of FIG. l, wherein the extractiveprocedure is carried out in multiple stages;

FIG. 3 is a diagrammatic showing of a process providing an alternativeembodiment of the invention and utilizing a solvent of the lowercritical solution temperature type;

FIG. 4 is a phase diagram for a selected solvent-water system, utilizingthe invention and having an upper critical solution temperature;

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FIG. 5 is a phase diagram similar to that of FIG. 4 but based on asolvent having a lower critical solution temperature; and

FIG. 6 is a diagrammatic showing of a system similar to that of FIG. 3,but based on a solvent of the upper critical temperature type.

If consideration is given to temperature-concentration relationships ofaqueous solutions of selected partially water soluble polymers with agiven solvent-polymer energy or" interaction such that a region of phaseseparation exists, there will lbe noted a strong degree of asymmetry inthe composition of the coexistent phases. Thus, the polymer rich phaseat a temperature somewhat below the critical phase separationtemperature, contains a large proportion of water, said 30-60%. On theother hand, the coexistent aqueous phase contains little or no polymersolvent.

For the selected polymer solvent, as the temperature is decreased, themu-tual solubility of polymer and water in the two phases decreases, butfor the aqueous phase, the solubility of polymer rapidly decreases to anorder of magnitude of parts per million of water. The presence oi' saltin the aqueous phase (3-7%) does not materially alter the nature of agiven temperature-concentration relationship for a given polymer solventexcept to clis-l place the curve slightly upward so as to increase thecritical phase separation temperature by Ia few degrees.

Thus, it has been found that by proper combination of hydrophilic and'hydrophobic monomers; copolymers are formed which will provide variousdesired temperature-concentration relationships. The shape of such curvemay be further modified by the adjustment of the molecular weight of the'copolymer land the exact degree of hydrophiiia fand hydrophobia of theconstituent monomers. This is usually indicated by the dielectricconstant of the copolymer. Furthermore, three or more monomers may becopolymerized for additional adjustment of the desired curve.

Accordingly, in accordance with the instant invention, water of reducedsaline content may be extracted from sea water or brackish water in asingle stage of operation or by multiple stages operatingcountercurrently with the salt containing water passing through thesuccessive stages to progressively augment its original salt contentwhile simultaneously losing a portion of its water content to a polymersolution passing through the stages land thus increasing the watercontent of the polymer solution.

In such countercurrent operation, it is advantageous to have operationaltemperatures changing from` stage to stage with the saline stream givingup heat to the polymer rich stream, thus Iachieving a considerablereduction in heat requirements.

In either the single or multiple stage operation, extraction takes placeat elevated temperatures which may be a few degrees less than the uppercritical solution temperature of the selected polymer solvent in respectto water or salt containing water, thereby giving .a solvent extractsaturated with saline free water. Cooling the extract by countercurrentheat exchange with incoming salt containing water., to a determinedtemperature will result in phase sepa-ration to provide an aqueous phasecontaining less than two parts per million of dissolved polymer solvent;and a polymer rich phase which may be recycled through the extractivestage or stages of the process.

Essentially, the process of the instant invention involves the use ofselected low molecular weight, low viscosity copolymers which arepartially water soluble; the aqueous solution of such copolymers havinga high extractive power for water at certain critical temperatures; thewater enriched solutions being subject to phase separation at othercritical temperatures to provide a water phase which is substantiallyfree of copolymer and thus available as a potable product; and a polymerrich phase for recycling `for further extractive operations.

More particularly, the selected polymer solvent which has a molecularweight of at least about 5,000 has an upper critical solutiontemperature, i.e., the polymer is completely miscible with water abovesuch temperature; and at temperatures below said critical temperature,will separate into (1) a phase which is relatively rich in polymer (overpolymer) and (2) an aqueous phase which is practically devoid ofpolymer. As the temperature is lowered relative to said criticalSolution temperature, the aqueous phase exhibits progressively reducedproportions of polymer which asymptotically approach zero.

On the other hand, the coexistent polymer rich phase will concurrentlybecome richer in its polymer content and may rise to over 40%.

Further, certain selected polymer solvents may exhibit lower criticalsolution temperatures such that at temperatures below such criticaltemperature, the miscibility of the polymer in water will be complete inall proportions, but with increasing temperatures above said criticalsolution temperature there will be two coexistent phases: (l) an aqueousphase which will show decreasing concentrations of polymer; and (2) apolymer rich phase which will show increasing polymer proportions withincreasing temperatures.

In FIG. 1 is shown a single stage system embodying the invention andutilizing a solvent of the upper critical solution tem erature type,wherein 10 designates a supply line carrying Water having a salinecontent, and may be sea water or brackish water. The temperature of thewater in line 10 is raised from about 20 C. to about 40 C. by passingthe same through a heat exchanger 11. From exchanger 11, the waterpasses in line 12 with an injection of low pressure steam at 13 to raisethe temperature thereof to about 45 C.

Line 12 is joined by a supply line 14 carrying an aqueous solution ofpartially water soluble copolymer, hereinafter described in detail,which is at a temperature of about 45 C., low pressure steam 4beinginjected into line 14 and 15. rlfhe mixture of saline water andcopolymer solution pass into a mixer-extraction tank 16, by Way of amixing chamber 17 thereof and thence into a settling chamber 18 thereof.

In tank 16, the copolymer solution will extract water from the salinesolution to form a lower stratum 19 of Water enriched solvent solutionand an upper stratum 20 of saline solution having an increasedproportion of salt. The lower stratum 19 passes from tank 16 by way ofline 21 and pump 22 at its elevated temperature to heat exchanger 11Where its heat is given up to raise the temperature of the incoming saltcontaining water in supply line 10, thus cooling the polymer solution toabout C. and passing by line 23 to a separator tank 24.

At the indicated reduced temperature, the copolymer solution enriched asto its water content, undergoes phase separation to provide an upperstratum 25 of water substantially free of copolymer, the polymer contentbeing less than 5 parts per million of Water; and is drawn otlin productline 26.

In tank 24 there is also formed a lower stratum 27 of an aqueoussolution of copolymer solvent which is solvent rich and `passes by line28 and pump 29 to a line 30 to a pair of heat exchangers 31, 32 wherethe temperature of the solution is raised to about 40 C.; exchanger 31receiving a portion of water enriched solvent from line 21 at atemperature of about 45 C. From exchanger 31, the copolymer solutionpasses to line 14, as previously described, to recycle and extractsubstantially saline free water from water having a salt content in tank16.

The upper stratum 2t) of salt enriched water passes [rom tank 16 by wayof line 33 and pump 34 at a temperature of about 45 C. to heat exchanger32 to give up its heat to raise the temperature of a portion of thesolvent rich copolymer in line 33. The salt water leaving exchanger 32which may have a slat content of about 6-7% now passes directly towaste, or alternatively, may pass to a heat exchanger 35 for cooling toabout 25 C. and thence to a separator tank 3-6 where residual copolymersolution will separate as a lower layer 37 to pass by line 3S and pump39 to separator tank 24 for further recovery of copolymer solvent. Thesalt rich upper layer 40 in tank 36 may now pass to waste by line 41.

Another portion of water enriched solvent from line 21 at 457 C. passesby line 42 through heat exchanger 31, as previously described, coolingthe same to about 30 C. and then passes to a heat exchanger 43 which iscooled by a salt water line 44 at 20 C., to about 25 C. and passes byline 45 to line 23 and thence to separator 24 for phase separation aspreviously described. Heat exchanger 35 is similarly cooled by saltWater at 20 C. in line 46.

rThe separatory and extractive procedure using a solvent of the uppercritical solution temperature type may also be carried out in multiplestages, as shown in FIG. 2. Here the salt containing water or sea wateris progressively treated in successive extractive tanks with copolymersolvent solution in countercurrent relation, whereby the solventsolution is progressively enriched with water while the saline solutionprogressively increases its saline content. The water enriched solventsolution is then subjected to phase separation to provide a potablewater having little or no saline content and copolymer solution forrecycling in the system.

Thus, as shown in FIG. 2, salt containing water at 20 C. in feed line 10passes through heat exchanger `11 to have its temperature raised toabout 40 C. and thence by line 12 and steam injector 13 at a temperatureof about 45 C. to meet copolymer solvent solution in a supply line 14Afor mixture and extraction in tank 16A, similar to tank 16 previouslydescribed. The Water enriched layer 19A in tank 76A passes by line 21and pump 22 to heat exchanger 11 for cooling to a temperature of about25 C. for phase separation in tank 24, Where the aqueous phasesubstantially free of copolymer solvent passes as product by line 26.

The copolymer solvent phase 2.7 in tank 24 is recycled by line 28 andpump 29 to line 30A and thence to heat exchanger 31 for raising itstemperature, through a portion of the hot, water enriched copolymersolution passing from line 21 through said exchanger. From exchanger 31,the copolymer solution passes to heat exchanger 50 by way of line 51 tobe heated to about 40 C. and thence by line 14C to meet salt containingWater in line 33B for extraction in the third stage tank 16C, lowpressure steam being injected at 15 to 'bring the combined streams to atemperature of about 45 C.

The lower stratum 19C of water rich copolymer solution in tank 16Cpasses to line 14B to meet saline enriched water in line 33A fromextraction tank 16A, for extracting water therefrom in tank 16B wherethe lower stratum 19B of copolymer solution passes to line 14A. Lowpressure steam may be injected at appropriate points in the system tomaintain the extraction temperature of about 45 C. for the selectedcopolymer solution.

It will be apparent that as the copolymer solution passes through thesuccessive extraction tanks 15C, 16B and 16A, the proportion of waterthereof will progressively increase while the salt containing waterpassing through said extraction tanks will show a progressive increasein its saline content. Thus in the case of the treatment of sea water,the water leaving tank 16C with a saline content of 6-7% and at atemperature of about 45 C., passes by line 52 and pump 53 to be cooledin heat exchanger 50 to about 30 C. and thence to a heat exchanger 54cooled 1y a sea water line 55 to about 25 C. and thence to a separatortank 36 where any copolymer solution will separate out as a lower layer37 and which passes to heat exchanger 50 via line 38 and pump 39 forrecycling in line 14C.

In the systems shown in FIG. l and FIG. 2, using a sea water feed pumpedat a rate of about 2000 gallons/hr. with 1000 gallons/h1'. of salinefree water being extracted to pass in product line 26; 1000 gallons/hr.of salt enriched sea water from upper layer 40 in tank 36 will pass towaste by way of line 41. About 2500 gallons/hr. of concentratedcopolymer solution is used in the extractive process; small amounts ofnew copolymer solution being added periodically to make up for losses inthe cycling procedure.

The copolymer solution used for extraction and phase separation isselected so as to have a desired phase separation relation in respect towater in terms of temperature and concentration differentials. To thisend, the copolymer is derived from hydrophilic and hydrophobic monomerscopolymerized to produce a low molecular weight product of lowviscosity.

Thus, the copolymer used in the single and multiple stage systemsdescribed above, may be formed by copolymerizing 30 parts of vinylalcohol with 70 parts of methyl vinyl ketone, all by weight- Such acombination will exhibit a concentration-temperature relationship asshown in FIG. 4, wherein the copolymer at 45 C. with a concentration of40% can take on 'water to reduce the copolymer concentration to about28.3% at C., phase separation takes place to restore the copolymerconcentration to 40% as indicated. This copolymer applicable to thesystems of FIGS. 1, 2 is of the upper critical solution temperaturetype.

Another example of copolymer of the upper critical solution temperaturetype, would be made by copolymerizing 50 parts of maleic acid diester ofpropylene glycol and butyl alcohol, with 50 parts of maleic acid diesterof propylene glycol and octyl alcohol. lIn another example, the solventis made by copolymerizing 80 parts of propylene glycol methacrylate and20 parts of methyl methacrylate.

Various other combinations of monomers may be copolymerized to provide asolvent of the upper critical solution temperature type, using electedproportions of (A) vinyl alcohol or maleic acid diester of propyleneglycol and butyl alcohol, or propylene glycol methacrylate, or methylvinyl ether; and (B) methallyl alcohol, or methyl vinyl ketone, ormaleic acid diester of propylene glycol and octyl alcohol, or methylmethacrylate, or acrylonitrile, or styrene.

For making copolymer solvents of the lower critical solution temperaturetype, monomers selected from the group (A) vinyl pyrrolidone,acrylamide, ethyleneimine, hexamethylene imine, vinyl carbazole, may becopolymerized with monomers selected from group (B) above, or vinylpyridine. A typical temperature concentration curve for this type ofcopolymer is shown in FIG. 5 wherein the copolymer is made bycopolymerizing 50 parts of vinyl pyrrolidone with 50 parts of vinylpyridine, all by lweight.

In addition, partially substituted cellulose ethers such as the methylor ethyl ethers may be used as solvent of the low critical solutiontemperature type. In such ethers the degree of substitution is 0.15 to0.30 ether groups per glucose unit.

It is understood that the selection of two, three or more monomers fromthe groups A and B, above, the temperature-concentration curve may beadjusted as desired. Preferably, the copolymer should be of lowmolecular lweight, ranging from about 5,000 to about 10,000; althoughthe range may encompass Weights of from 3,000 to about 20,000. Also, theviscosity of the copolymers should be of a relatively low order ofmagnitude for optimum operation of the systems.

Variations in temperature of the incoming saline feed may requireadjustment in the nature of the copolymer solvent used, as by adjustingthe proportions of the monomer making up the copolymer.

In FIG. 3 is shown an alternative form of single stage extraction andseparation system using solvents of the lower critical solutiontemperature type, wherein the supply line 10 carrying salt containingwater such as 3.5% salt containing sea water is mixed with a selectedconcentrated copolymer solvent at about 75 F. in line 14 and passed to aconventional Podbielnak centrifuge separator 60 which rotates about ahorizontal axis in a known manner, by way of an input port 61 thereon.

Wash `water from product line 26 also passes into sepator 60 at 75 F.,by Way of line 62, while water enriched copolymer solution leavesseparator 60 by Way of line 63 passing to a heat exchanger 64 Where thetemperature of the solvent is raised to about 103 F. and thence by aline 65 to a heat exchanger 66 heated by exhaust steam, to furtherincrease the temperature of the water enriched copolymer to about 110F., which then passes to separator tank 16.

In tank 16, phase separation occurs with a lower stratum 19 ofconcentrated copolymer solution passing by way of line 21 and pump 22 toheat exchanger 64 Iwhere the same is cooled to 84 F. and thence passesto a heat exchanger to eifect a further cooling to about 75 and thenceby way of line 14 to the separator 60. The upper stratum 20 in tank 16comprising water substantially free of solvent, passes by Way of line 33and pump 34 to heat exchanger 64 where the temperature is reduced toabout 82 F. and thence to a heat exchanger 68 where the temperature isfurther reduced to about 75 F. and thence passes to product line 26, aportion thereof providing wash water for line 62.

The Podbielniak separator 60 is highly eiective in washing the waterrich copolymer solution free of salt and the concentrated salt solutionhaving up to 7% salt passes from separator 60 to waste by way of line70.

In FIG. 6 is shown a modification of the system of FIGS. l, 2, based ona solvent of the upper critical solution temperature type. Here thesaline feed line 10, carrying sea water with a salt content of 3.5%, at68 F. passes by Way of pump 10A to heat exchanger 11 Where thetemperature of the feed is raised to 78 F., and then passes to a secondheat exchanger 11A where the temperature of the feed is raised to 103 F.and then passes to a third heat exchanger 11B, operating with exhauststeam, Where the temperature of the feed is further raised to 1l6.6 F.

The feed from heat exchanger 11B is supplied to the input side of aPodbielniak centrifuge separato-r 60, as previously described inconnection with FIG. 3, together with a solvent of the upper criticalsolution temperature type brought in by line 62,

Water enriched solvent leaves separator 60 by line 63 at a temperatureof 110 F., and passes through heat exchangers 11A, 11 whereby thetemperature thereof is reduced successively to F. and 75 F., and thenpasses to separation tank. Here the upper stratum 20 of potable waterpasses to product line 33.

The lower stratum 19 in tank 20 of lean solvent, passes by line 22 toheat exchanger 32 where the temperature thereof is raised from 75 to 102F. and then passes to line 63A to join the saline feed in line 10 atl16.6 F. to provide a mixture at 1l0.2 F. for admission to centrifugeseparator 60.

Centrifuge 60 is provided with wash Water from a line 62 extending fromstratum 20 of tank 16, by way of heat exchanger 11A which raises thetemperature of such Wash water from 75 F. to 103 F.

A portion of the mixture of solvent and water from centrifuge 60 passesby way of line 63B to heat exchanger 32 and thence at a reducedtemperature of 85 F. to heat exchanger 11.

Water of increased saline content (7.0%) passes out of centrifuge 60 byway of line 70 at 110 F., thence through heat exchanger '32 where thetemperature thereof is reduced to 82 F. and thence to a heat exchanger68 cooled by water at 68 F., to a temperature of 75 F. The waste 'Z7products then pass to a separator tank loA where residual solvent inlower stratum 19A passes to line 22, while the high saline content waterfrom upper stratum ZdA passes out by waste line 70A.

What is claimed is:

l. The method of reducing the salt content of salt containing watercomprising mixing such water with aqueous solution of a polymericsolvent compound, said solvent compound being used in an amount tomaintain solution in a liquid state at all times, at a given temperatureto form a liquid body having a stratum of water enriched solventcompound solution and a stratum of sait enriched water, drawing off thestratum of water enriched solvent compound solution and changing thetemperature thereof with respect to said given temperature whereby saidwater enriched solution forms an aqueous phase substantially free ofsolvent compound and an enriched solvent liquid phase, and drawing oitsaid aqueous phase.

2. The method of claim 1 wherein the polymeric solvent compound isselected from the group consisting oi partially substituted ethyl andmethyl cellulose ethers and low molecular weight partially water solublecopolymers of hydrophilic and hydrophobic monomers and wherein thehydrophilic monomer of said copolymer is selected from the groupconsisting of vinyl alcohol, maleic acid diester of propylene glycol andbutyl alcohol, propylene glycol methacrylate, methyl vinyl ether, vinylpyrrolidone, acrylamide, ethyleneimine or vinyl carbazole; andthehydrophobic monomer of said copolymer is selected from the groupconsisting of methallyl alcohol, methyl viny ketone, maleic acid diesterof propylene glycol and octyl alcohol, kmethyl methacrylate,acrylonitrile, styrene and vinyl pyridine.

3. The method as in claim l wherein said polymeric solvent compo-und hasa molecular weight of from about 3,000 to about 20,000.

4. The method as in claim l wherein said stratum of salt enriched wateris drawn off and the temperature thereof changed to cause separation ofany residual solvent compound solution and recovering said solventcompound solution.

5. A method as in claim l wherein said given temperature is somewhatless than the critical phase separation temperature of said aqueoussolvent compound solution to extract water from said salt containingwater and to increase the Water content of said solvent compoundsolution while increasing the salt content of said salt containingWater, reducing the temperature of the water enriched solvent compoundsolution to a point Where said solution separates into an aqueous phasesubstantially free of solvent compound and a solvent compound richliquid phase, and drawing ot said aqueous phase.

6. A method as in claim 1 wherein said mixture of salt containing waterand solvent compound solution is washed with water while subjected tocentrifugation to provide said stratum ot water enriched solventcompound solution and said stratum of salt enriched water.

7. A method as in claim` l wherein the solvent compound of said solventcompound solution is completely miscible with water at temperaturesabove said given temperature, and at temperatures below said giventemperature, said solvent compound solution will separate into anaqueous phase and a solvent compound liquid phase.

A method as in claim l wherein the solvent compound of said solventcompound solution is completely miscible with water at temperaturesbelow said given temperature, and at temperatures above said giventemperature, said Solvent compound solution will separate into anaqueous phase and a solvent compound liquid phase.

9. A method as in claim l wherein said salt containing water and saidsolvent compound solution are passed in d countercunrent mixing relationthrough successive extraction stages to form in each stage a layer owater enriched solvent compound solution and a salt enriched waterlayer, the water content of the water enriched solvent compound solutionincreasing progressively in the successive stages While the salt contentof the salt enriched water layers increase progressively in thesuccessive stages, removing the Water enriched solvent compound solutionfrom the stage having the maximum water content, changing thetemperature of the last mentioned solvent compound solution to a valueeffective to cause phase separation therein providing an aqueous phasesubstantially free of solvent compound solution and an aqueous enrichedsolvent compound solution phase and drawing ott said aqueous phase.

l0. A method as in claim 9 and further including the step of removingthe salt enriched Water layer :from the stage of maximum salt content,changing the temperature thereof to a value wherein any residualpolymeric solvent compound solution will separate from the salt enrichedwater layer, and recovering said residual solvent compound solution.

lll. The method of desalinating sea water comprising mixing sea waterwith an aqueous solution of low molecular weight partially water solublecopolymer of hydrophilic and hydrophobic monomers at an elevatedtemperature to form a stratum ot' water enriched copolymer solution anda stratum of sea water of increased saline content, drawing off thestratum of water enriched copolymer solution and reducing thetemperature thereof to a point wherein said solution forms an aqueousphase substantially free of copolymer and `an enriched copolymer phase,`and drawing oh said aqueous phase.

l2. The method of claim lll wherein said copolymer has a molecularweight of from about 3,000 to about 20,000.

13. The method of claim 1l wherein said stratum of sea Water ofincreased saline content is drawn off and reduced in temperature tocause separation of any residual copolymer solution and recovering saidcopolymer solution.

ll4l. A method of desalinating sea water comprising passing sea waterand an aqueous solution of partially water soluble, low molecular weightcopolymer formed of hydrophilic and hydrophobic monomers, incountercurrent mixing relation through successive extraction stages toform in each stage a layer of water enriched copolymer solution and alayer of salt enriched sea water, the water content of the waterenriched copolymer solution increasing progressively in the successivestages while the salt content of the sea water layer is increasingprogressively in the successive stages, removing the water enrichedcopolymer solution from the stage having the maximum water content,reducing the temperature of the last mentioned copolymer solution tocause phase separation thereof into an aqueous phase substantially freeof copolymer and an aqueous enriched copolymer phase, and drawing olfsaid aqueous phase.

i5. A method as in claim i4 and further including removing the saltenriched sea water layer from the stage of maximum salt content,reducing the temperature of said enriched sea water layer to a pointwherein any residual copolymer solution will separate out, andrecovering said residual copolymer solution.

i6. A method of desalinating sea water comprising mixing sea water andan aqueous solution of partially water soluble, low molecular weightcopolymer formed from a hydrophilic monomer and a hydrophobic monomer ata given elevated temperature somewhat less then the critical phaseseparation of said aqueous solution of copolymer to extract water fromthe sea water and to increase the water content of said copolymersolution while increasing the salt content of the sea water, separatingthe water enriched copolymer solution from the salt enriched sea water,reducing the temperature of the 9 10 Water enriched copolymer solutionto a point where said References Cited solution separates into a Waterphase substantially free UNITED STATES PATENTS of co ol er yand a co 0lmer lric-l1 hase, and drawi Off d gluem phase? y P g 3,234,126 2/1966Bioch 21o-59 17. A method -as in claim 16 wherein said copolymer 5 has amolecular weight of from about 5,000 to about 10,000.

MICHAEL E. ROGERS, Primary Examiner.

1. THE METHOD OF REDUCING THE SALT CONTENT OF SALT CONTAINING WATERCOMPRISING MIXING SUCH WATER WITH AN AQUEOUS SOLUTION OF A POLYMERICSOLVENT COMPOUND, SAID SOLVENT COMPOUND BEING USED IN AN AMOUNT TOMAINTAIN SAID SOLUTION IN A LIQUID STATE AT ALL TIMES, AT A GIVENTEMPERATURE TO FORM A LIQUID BODY HAVING A STRATUM OF WATER ENRICHEDSOLVENT COMPOUND SOLUTION AND A STRATUM OF SALT ENRICHED WATER, DRAWINGOFF THE STRATUM OF WATER ENRICHED SOLVENT COMPOUND SOLUTION AND CHANGINGTHE TEMPERATURE THEREOF WITH RESPECT TO SAID GIVEN TEMPERATURE WHEREBYSAID WATER ENRICHED SOLUTION FORMS AN AQUEOUS PHASE SUBSTANTIALLY FREEOF SOLVENT COMPOUND AND AN ENRICHED SOLVENT LIQUID PHASE, AND DRAWINGOFF SAID AQUEOUS PHASE.